1. Field of the Invention
The invention relates to a piston for an internal combustion engine with a profiled ring groove.
More particularly, this invention relates to a piston where at least one surface of a compression ring groove is provided with profiling extending circularly around the longitudinal piston axis.
2. Description of the Prior Art
Internal combustion engines, and specifically Otto-cycle engines are known which have pistons made of light metal alloys. During the initial break-in period of these engines, the groove surfaces can be damaged, particularly in the upper most compression ring groove. In order to prevent excessive wear, these grooves have been surface-coated, which is a costly process.
German patent DE-OS 39 03 722 discloses a piston for an internal combustion engine in which the ring groove is treated in order to prevent the piston ring from sticking to the aluminum alloy of the piston without increasing the amount of gasoline blow-by or oil consumption. At least one of the lower groove surfaces of the uppermost compression ring grooves is subjected to a surface-hardening treatment (anodizing treatment) so that the roughness of the surface is increased. The surface of the piston ring, disposed opposite the hardened surface, is provided with a resin coating which provides excellent adhesive properties. One disadvantage of this method is that the anodizing treatment produces a non-uniform rough surface on the lower groove side, and the piston rings require an additional coating.
U.S. Pat. No. 5,083,536 discloses large radial recesses distributed over the circumference of the top surface of the upper compression groove. The combustion gases can exert an intense force on the uppermost piston ring to press it against the lower groove surface.
However, the prior art does not disclose a simple way to prevent damage to the groove surfaces.